Re: [PATCH v2] drm/i915: Fix races on fbdev

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Mar 09, 2016 at 12:52:53PM +0100, Lukas Wunner wrote:
> The ->lastclose callback invokes intel_fbdev_restore_mode() and has
> been witnessed to run before intel_fbdev_initial_config_async()
> has finished.
> 
> We might likewise receive hotplug events before we've had a chance to
> fully set up the fbdev.
> 
> Fix by waiting for the asynchronous thread to finish.
> 
> v2:
> An async_synchronize_full() was also added to intel_fbdev_set_suspend()
> in v1 which turned out to be entirely gratuitous. It caused a deadlock
> on suspend (discovered by CI, thanks to Damien Lespiau and Tomi Sarvela
> for CI support) and was unnecessary since a device is never suspended
> until its ->probe callback (and all asynchronous tasks it scheduled)
> have finished. See dpm_prepare(), which calls wait_for_device_probe(),
> which calls async_synchronize_full().
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93580
> Reported-by: Gustav Fägerlind <gustav.fagerlind@gmail.com>
> Reported-by: "Li, Weinan Z" <weinan.z.li@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: stable@vger.kernel.org
> Signed-off-by: Lukas Wunner <lukas@wunner.de>

Queued for -next, thanks for the patch.
-Daniel

> ---
>  drivers/gpu/drm/i915/i915_dma.c    | 8 +++-----
>  drivers/gpu/drm/i915/intel_fbdev.c | 3 +++
>  2 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index 4aa3db6..9d76dfb 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -430,11 +430,9 @@ static int i915_load_modeset_init(struct drm_device *dev)
>  	 * Some ports require correctly set-up hpd registers for detection to
>  	 * work properly (leading to ghost connected connector status), e.g. VGA
>  	 * on gm45.  Hence we can only set up the initial fbdev config after hpd
> -	 * irqs are fully enabled. Now we should scan for the initial config
> -	 * only once hotplug handling is enabled, but due to screwed-up locking
> -	 * around kms/fbdev init we can't protect the fdbev initial config
> -	 * scanning against hotplug events. Hence do this first and ignore the
> -	 * tiny window where we will loose hotplug notifactions.
> +	 * irqs are fully enabled. We protect the fbdev initial config scanning
> +	 * against hotplug events by waiting in intel_fbdev_output_poll_changed
> +	 * until the asynchronous thread has finished.
>  	 */
>  	intel_fbdev_initial_config_async(dev);
>  
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index ae9cf6f..7e73acc 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -800,6 +800,8 @@ void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous
>  void intel_fbdev_output_poll_changed(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> +
> +	async_synchronize_full();
>  	if (dev_priv->fbdev)
>  		drm_fb_helper_hotplug_event(&dev_priv->fbdev->helper);
>  }
> @@ -811,6 +813,7 @@ void intel_fbdev_restore_mode(struct drm_device *dev)
>  	struct intel_fbdev *ifbdev = dev_priv->fbdev;
>  	struct drm_fb_helper *fb_helper;
>  
> +	async_synchronize_full();
>  	if (!ifbdev)
>  		return;
>  
> -- 
> 1.8.5.2 (Apple Git-48)
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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